Sorption and partial molar volumes of C2 and C3 hydrocarbons in polypropylene copolymers

The sorption of C₂ and C₃ hydrocarbons in two ethylene–propylene copolymers and a propylene homopolymer and the simultaneous dilation of the polymers were measured at temperatures of 287–363 K and pressures up to 4 MPa. The sorption isotherms were well described by the Flory–Huggins theory of dissolution. Dilation isotherms in the form of elongation versus pressure were similar in shape to the corresponding sorption isotherms. Solubility coefficients, partial molar volumes, and Flory–Huggins interaction parameters were determined from these isotherms. The thermal expansivities of the hydrocarbons dissolved in the polymers were 0.002–0.005 K^?1, and the Flory–Huggins interaction parameters depended not only on temperature but also on concentration. At 323 K, the calculated solubilities of propylene in the ethylene–propylene‐rubber regions of the copolymers were 1.8 times higher than in the amorphous regions of the propylene homopolymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1255–1262, 2001     

Control of high-k/germanium interface properties through selection of high-k materials and suppression of GeO volatilization

Two approaches to control high-k/Ge interface qualities were investigated. The first approach was using high-k materials that are intimate with Ge. These Ge-intimate high-k materials should have moderate reactivity with Ge to form an amorphized interface that will reduce the interface defects and will suppress the GeO desorption at the interface. The second approach was modifying the annealing processes by using a cap layer to block GeO out-diffusion. We found that Si works as the cap layer very efficiently. By combining those two approaches, we achieved fairly good high-k/Ge metal-insulator-semiconductor (MIS) characteristics with LaYO₃ as the Ge-intimate high-k material, and a NiSi_X electrode as the cap layer. These results provide us an important guide for controlling the high-k/Ge interface properties.     

Luminescence enhancement of Eu, Ce co-doped Ba3Si5O13−δNδ phosphors

Host lattice Ba₃Si₅O_13−δN_δ oxonitridosilicates have been synthesized by the traditional solid state reaction method. The lattice structure is based on layers of vertex-linked SiO₄ tetrahedrons and Ba²⁺ ions, where each Ba²⁺ ion is coordinated by eight oxygen atoms forming distorted square antiprisms. Under an excitation wavelength of 365 nm, Ba₃Si₅O_13−δN_δ:Eu²⁺ and Ba₃Si₅O_13−δN_δ:Eu²⁺,Ce³⁺ show broad emission bands from about 400-620 nm, with maxima at about 480 nm and half-peak width of around 130 nm. The emission intensity is strongly enhanced by co-doping Ce³⁺ ions into the Ba₃Si₅O_13−δN_δ:Eu²⁺ phosphor, which could be explained by energy transfer. The excitation band from the near UV to the blue light region confirms the possibility that Ba₃Si₅O_13−δN_δ:Eu²⁺, Ce³⁺ could be used as a phosphor for white LEDs.     

Evolution of the Kondo effect in a quantum dot probed by shot noise

We measure the current and shot noise in a quantum dot in the Kondo regime to address the nonequilibrium properties of the Kondo effect. By systematically tuning the temperature and gate voltages to define the level positions in the quantum dot, we observe an enhancement of the shot noise as temperature decreases below the Kondo temperature, which indicates that the two-particle scattering process grows as the Kondo state evolves. Below the Kondo temperature, the Fano factor defined at finite temperature is found to exceed the expected value of unity from the noninteracting model, reaching 1.8±0.2.     

Comparison of reactivity on step and terrace sites of Pd (3 3 2) surface for the dissociative adsorption of hydrogen: A quantum chemical molecular dynamics study

The notion of “active sites” is fundamental to heterogeneous catalysis. However, the exact nature of the active sites, and hence the mechanism by which they act, are still largely a matter of speculation. In this study, we have presented a systematic quantum chemical molecular dynamics (QCMD) calculations for the interaction of hydrogen on different step and terrace sites of the Pd (3 3 2) surface. Finally the dissociative adsorption of hydrogen on step and terrace as well as the influence of surface hydrogen vacancy for the dissociative adsorption of hydrogen has been investigated through QCMD. This is a state-of-the-art method for calculating the interaction of atoms and molecules with metal surfaces. It is found that fully hydrogen covered (saturated) step sites can dissociate hydrogen moderately and that a monovacancy surface is suitable for significant dissociative adsorption of hydrogen. However in terrace site of the surface we have found that dissociation of hydrogen takes place only on Pd sites where the metal atom is not bound to any pre-adsorbed hydrogen atoms. Furthermore, from the molecular dynamics and electronic structure calculations, we identify a number of consequences for the interpretation and modeling of diffusion experiments demonstrating the coverage and directional dependence of atomic hydrogen diffusion on stepped palladium surface.     

A case of Budd-Chiari syndrome: Gd-EOB-DTPA-enhanced MR findings

Budd-Chiari syndrome (BCS) is a rare disorder caused by the obstruction of hepatic venous outflow, leading to sinusoidal congestion, ischemic injury to liver cells and portal hypertension. Long-term survival largely depends on whether hepatocellular carcinoma occurs. A recently available liver-specific contrast medium, gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid (Gd-EOB-DTPA), reportedly has high diagnostic capability for detection of malignant liver tumors. However, there has been no report of the sue of Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) for BCS. We present a case of chronic BCS who underwent both gadopentetate dimeglumine (Gd-DTPA) and Gd-EOB-DTPA-enhanced MRI. Hepatic congestion and edema were seen as slightly hypointense areas on Gd-EOB-DTPA-enhanced hepatobiliary-phase images, although these areas were observed as slightly hyperintense on previously obtained Gd-DTPA-enhanced delayed-phase image. Reduced uptake of Gd-EOB-DTPA by hepatocytes in the region of congestion or edema may account for this difference, which should be recognized in image interpretations.     

An ab initio-based approach to the stability of GaN(0 0 0 1) surfaces under Ga-rich conditions

Structural stability of GaN(0 0 0 1) under Ga-rich conditions is systematically investigated by using our ab initio-based approach. The surface phase diagram for GaN(0 0 0 1) including (2×2) and pseudo-(1×1) is obtained as functions of temperature and Ga beam equivalent pressure by comparing chemical potentials of Ga atom in the gas phase with that on the surface. The calculated results reveal that the pseudo-(1×1) appearing below 684–973 K changes its structure to the (2×2) with Ga adatom at higher temperatures beyond 767–1078 K via the newly found (1×1) with two adlayers of Ga. These results are consistent with the stable temperature range of both the pseudo-(1×1) and (2×2) with Ga adatom obtained experimentally. Furthermore, it should be noted that the structure with another coverage of Ga adatoms between the (1×1) and (2×2)-Ga does not appear as a stable structure of GaN(0 0 0 1). Furthermore, ghost island formation observed by scanning tunneling microscopy is discussed on the basis of the phase diagram.     

On the use of nickel foil strain gages at varying temperatures

When a strain gage made of nickel foil attached on the surface of a specimen is subjected to repeated loads, the elastic stress is measured by observing slip-bands in the foil resulting from repeated strain. Calibration studies with rotating-bending tests at various temperatures between room temperature and 350°C are performed on round steel bars with nickel foil. The relation between the threshold stress for the first appearance of slip-bands and the number of stress cycles is examined at varying temperatures, which provides the calibration values of the nickel foil tested at varying temperatures. Assuming that the first appearance of slip-bands is based on the linear cumulative damage law, the calibration values at varying temperatures are calculated from those established by the calibration tests at several constant temperatures. It is found that the calculated calibration values agree well with the results obtained by the calibration tests at varying temperatures and that the calculation applying the linear cumulative damage law is a useful method to presume the calibration values at varying temperatures without performing the experiment.